Include `includeSubgroups: true` when querying groups

As reported in gitlab-org#14939 (comment 2082563187), Querying for issues in a group only returns issues from projects directly under the group and not any sub-groups.

We should add includeSubgroups: true to the issues(...) call when a group is specified in the current context.

query{
  group(fullPath:"gitlab-org"){
    issues(includeSubgroups:true){
      nodes { iid title webUrl }
    }
  }
}